It is clear that the Internet, which is the widest of all wide area networks, is the most important development in computing and communications in modern history. The Internet allows home and business computers located throughout the world to communicate with each other. Communication between these computers is possible as the result of the connection of many large computer networks tied together to form the Internet. Modern advancements have resulted in the development of very high speed equipment for use in carrying out Internet communications. The large computer networks that make up the Internet may be connected to each other using high speed backbone data links such as T-1, T-3, OC-1, and/or OC-3 links that are capable of transmitting data at rates on the order of megabits per second. It is also not uncommon for home computers to have processing speeds on the order of a gHz, and for businesses to have direct links to an Internet backbone.
Despite all these advances however, it has become painfully obvious that speed of communication over the Internet will always be limited by the speed of the slowest piece of equipment or communication link in the chain connecting the communication end points to the Internet backbone. Absent the special installation of a direct high-speed data link, such as a T-1 line, an end user PC's connection to the Internet is often initially made through the existing telephone line infrastructure. Existing telephone links comprise a twisted pair of copper wires running from each phone jack in a building to a local central office. Communication from the central offices to telephone switching centers is typically made with a higher speed link, such as an optical fiber connection. These higher speed links exist throughout the remainder of the network, but do not extend past the local central offices.
Presently, the most problematic bottleneck for Internet communication exists in the twisted copper pair link from a home or business PC to a traditional telephone central office. Twisted copper pairs were originally designed to carry analog communications, i.e., voice communication. In modern times however, communication needs have gone beyond just voice and require the transmission of data, preferably in a digital form. The technology to transmit digital data using an analog signal has existed for decades in the form of modem technology. As the years have gone by, modems have become faster and faster in an attempt to keep pace with the increase in the speed of other network components. Modem developers have finally reached an inherent limitation on the amount of data that can be carried on a twisted copper pair using an analog signal. This limitation arises from bandwidth constraints growing out of the fact that the analog channel used for modem communications is only 4 kHz wide. As a result, the best modems today are able to transmit data at a rate of 56 Kilobytes per second, provided that conditions are nearly perfect. With PC's operating at the GHz level and digital switches and T-1 lines operating at the MHz level, this clearly makes the modem based link between a home or business PC and the central office the slowest link in the Internet or other wide area network communication scheme. Accordingly, there is a need to provide a higher rate of communication over the existing infrastructure, namely the twisted pair of copper wires linking most homes and businesses with local central offices.
The desired higher rate communication over twisted copper pairs may be provided by a relatively new technology called Digital Subscriber Line (DSL) Technology, often referred to as xDSL where the x signifies different variations of DSL. DSL may allow the twisted copper pair to transmit digital information at rates between 128 kilobytes per second to as high as several megabytes per second. A detailed description of DSL Technology may be found in the publication “Personal Broad Band Services: DSL and ATM” by Jim Lane and published by Virata in 1998, which is hereby incorporated by reference.
The concept behind DSL is as follows. Voice communications over the twisted copper pair are carried out in a frequency range below 4,000 hertz because most human voices operate at less than 4 kHz. A twisted copper pair, however, is capable of transmitting higher frequency signals. The frequency range above 4 kHz, heretofore unused, can now be used by DSL equipment to send digital signals between homes and businesses and local central offices. What's more, because the DSL frequencies do not overlap with the voice frequencies, DSL communication and voice communication can occur simultaneously over the same copper pair facility.
There is a catch to the use of DSL, however. The higher frequency signals used to transmit DSL communications degrade as the distance between the end phone jack and the central office increases. This degradation is the product of both the distance and the increasing number of “taps” on the line that occurs with increasing distance. True highspeed DSL service (greater than 128 kbps) cannot be carried out when the “wire distance” between the end user and the central office is more than about three (3) miles. Luckily, central offices have been built throughout the United States such that most phone jacks are within a few miles “wire distance” of their respective central office.
As noted briefly above, in recent times there have also been important advances in the equipment (particularly in the switching technology and regimes) that is used at the central office and at other nodes further upstream headed towards the large Internet or other private networking hubs. Some of the most important advancements have involved packet type switching.
A packet is a generic term for a bundle of data that is organized in a specific way to facilitate its transmission over a network. Packets, also sometimes referred to as blocks, frames, or cells, primarily comprise three types of information: the payload, the header, and the trailer. Usually the largest part of a packet contains the payload, i.e., the data that is to be communicated. The header may be attached to the front of the payload. The header includes additional digital data that tells the network where the packet should be sent and in some instances the route that it should take. The trailer may contain data used to detect and correct errors in the payload that occur during transmission.
The broad category of packets may be further divided into subcategories of variable length packets and fixed length packets. The transmission of variable length packets is synonymous with “frame relay” transmission. Frame relay services employ a form of packet switching that is similar to that used for X.25 networks. In frame relay, the packets are in the form of frames that may vary widely in length between 0 and 4,096 octets. Because of the large variability in the size of “frame relay” frames, they are very suitable for the transmission of data that is not time sensitive. For example, frame relay is not well suited for the transmission of digital voice information because frames are designed to deliver large chunks of digital data but at less frequent intervals. Digital voice requires the transmission, at a regular pace, of little pieces of data that may be used to reassemble a voice communication after its transmission over at network. Frame relay applications most often include private data traffic transmission as a replacement to leased line services, such as T1.
Fixed length packets are the logical choice for digital data transmission when variable length packets are non-optimal. The most prevalent type of fixed length packets that are presently used are ATM packets which have a cell length of 53 bytes, 48 of which are for the payload. ATM is primarily used for LAN-to-LAN (Local Area Network) applications, carrier traffic aggregation and digital voice and video technology transmission. As a result, ATM packets are universally useful, and ATM compatible components are commonly used for highspeed networks, such as those that link with and comprise the Internet.
A significant number of end user PC's are equipped to carry out communications using Frame Relay protocol as opposed to ATM protocol. When these PC's are connected together on a local network with Frame Relay compatible components, they are able to easily communicate with each using Frame Relay packets. In modern times, however, there is an ever increasing need for end user PC's to communicate with other end users over wide area networks, including the Internet. Because these wide area networks are typically equipped with ATM compatible components, such as concentrators and switches, Frame Relay based communications could not be readily carried out over the wide area networks. In response to this problem, an industry group called the Frame Relay Forum (FRF) formulated standards to govern the transmission of Frame Relay packets over other broadband technologies, such as ATM based networks. The inventors of the present invention are familiar with three such standards in particular, FRF.5, FRF.8, and FRF.8.1, which pertain to standards for the transmission of Frame Relay packets and the interfacing of Frame Relay products with ATM based networks. These standards are available from the Frame Relay Forum, and are published in Frame Relay/A TM PVC Network Interworking Implementation Agreement FRF.5, The Frame Relay Forum (Dec. 20, 1994); Frame Relay/ATM PVC Network Interworking Implementation Agreement FRF.8, The Frame Relay Forum (Apr. 14, 1995); and Frame Relay/ATM PVC Service Interworking Implementation Agreement FRF.8.1, Frame Relay Forum Technical Committee (Feb. 28, 2000), each of which is incorporated herein by reference in its entirety.
In view of the importance of both DSL technology, and the transmission of Frame Relay communications over ATM based networks, for end-to-end high speed wide area and/or Internet communication, there is a need for a system and method that integrates DSL and Frame Relay over ATM network communications. To date, there have been some developments in integration of DSL with Frame Relay or ATM systems for aggregation purposes; however, there has not been a commercially successful marriage of all three.
An example of a DSL system that is adapted to transmit data through an ATM or a Frame Relay switch is described in U.S. Pat. No. 6,028,867 to Rawson et al. (Feb. 22, 2000), which is hereby incorporated by reference. The Rawson patent describes a network structure in which home PCs are connected to a Digital Subscriber Line Access Multiplexer (DSLAM) located in a central office. The DSLAM includes both an Asynchronous DSL (ADSL) multiplexer and an ISDN based DSL (IDSL) multiplexer. The IDSL multiplexer provides bandwidth of up to 128 kbps, but is not limited by the distance between the home PC and the central office. The ADSL multiplexer provides bandwidth of up to 6.1 Mbps in the direction from the central office to the home PC, and up to 640 kbps in the reverse direction so long as the local loop connecting the home PC to the central office is less than about 14,000 feet in length. The DSLAM is connected to a remote target (e.g. an Internet destination) through a generic data switch. The Rawson patent does not disclose a system or method for providing Frame Relay communication over an ATM based network that includes a DSL link.
Another example of a DSL system that is adapted to be used with a packet switched network is described in U.S. Pat. No. 6,081,517 to Liu et al. (Jun. 27, 2000), which is hereby incorporated by reference. The Liu patent discloses a broadband DSL service provider's network. Liu describes the equipment necessary to provide an end-user of a xDSL service with a connection at a greater speed than traditional remote access, or Internet access methods. The key differentiator in the Liu patent from the above-referenced Rawson patent and the below-referenced Fosmark patent is the description of a dynamic bandwidth allocation service on a “call by call” basis. The Liu patent states that end-users may dynamically request bandwidth from the network as the application needs change, and for those allocations to be based upon efficient network routing and cost models. Thus, from Liu it is inferred that the customer takes an active role in determining the cost to him/her based upon the bandwidth needed for the application being “called” from some content located on the network. Additionally, the Liu patent infers that the network dynamically chooses “the PSTN 250 or WAN 260, or setting up a virtual circuit via the WAN” based upon the needs of the end-user. While the Liu patent discloses a typical DSL link, generally, it does not disclose a DSL link that is capable of transmitting Frame Relay communications over an ATM equipped network.
Still another example of a DSL system is described in U.S. Pat. No. 6,084,881 to Fosmark et al. (Jul. 4, 2000), which is hereby incorporated by reference. The Fosmark patent discloses an endpoint (or CPE, Customer Premises Equipment) that uses an auto-negotiation function with the DSLAM to assign protocols associated with various packet and cell mode transmissions. Unlike the Liu and Rawson patents which describe an xDSL service provider's network, the Fosmark patent describes a specific piece of equipment in an xDSL network and is written on the behalf of an equipment manufacturer.
Therefore, there is a need for a system and method of connecting end users that employ Frame Relay communications to ATM host networks in a system that includes a DSL link. In response to these needs, the present applicants have developed a Frame Relay over xDSL product that may be used in association with an ATM based network.